Method for the preparation of zinc



.is the reoxidation of the .freshly reduced zinc. .and other disadvantages are substantially-diminished'by United States Patent James L. Wyatt, South Euclid, Ohio, assignorto Horiz'ons'Incorporated Application February 21, 1955 .Serial No. 489,783

"8--Clain1s. or. 75-86) .No Drawing.

This invention. relates to.a process: for producing. metallic zinc. Metallic zinc is commonly obtained from its ores by two.mainmethods: pyrometallurgical and-electrolytic. The pyrometallurgical; processes generally .de- .pendon thereduction. of zinc oxide to the metallicstat-e .by carbonaceous reducing gases in retorts, while in the .electrolytiqprocess,zinc ores are treated with.a suitable acid such as sulphuric acidand the resulting'zinc-containing solution is electrolyzed to recover the zinc. My invention -is..concerned .with .an .improvement in the pyrornetallurgical:recovery of zinc.

In therecent pastthe most widely employed :process .for the .pyrometallurgical recovery of zinc was a batch process. involving-the reduction ofra charge .of zinciferous material and carbon. Later-efforts have been directed toward thedevelopment of a-continuous'process. Possi- .bly'.the.most.recentprocessesevolved in-this artare the application of fluidized techniques illustrated in U. ;S. .Patent .No..2,478,912. Each-.ofthese prior -art,processes has been found to be .seriously limited in one or more respects. For instance thettendency of impurities usually associated withthe zinc-bearing rawrnaterialto fusetand agglomeratehas constituted the outstanding limitation of most. of. the-pyrometallurgical processes which have. been devised. Another problemencountered in the prior art These the ..practice .Of the process constituting the invention herein .disclosed. 1

.lnaccordance with my .invention athereduction of a zinc-bearingsource.materialais effected in a molten-salt menstruurn. -.By bringing .the zinciferous material into contact with areducing-gasimthis environment, advantagesare obtained which permit the reaction to-.be effected more.rapidly, .more efficiently-and at lower temperatures than was,.pos'sible .in theprior art processes. :In order that theadvantages of my :process may be better appreciated, abrief description of the present-day methods of producing zinc follows:

(a) Batch process.-The present typical batch type .process.is.conducted in a-plurality of externally-heated clay retorts-.6 to .12 inches in diameter .and up to 10 product .and low yield. As a result-.a-numberofucontinuousgproeesses have been suggested.

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(b) Continuous pr0cesses.-The above described batch process led to the development of :a continuous vertical retort-process, described in detail in volume 121 of the' Transactions of the A. I. M. .E. beginning .on page 427. Briefly, --a charge ,mixture consisting :of oxide ore or .roasted concentrate, binder and carbonaceous reducing material is briquetted. Thenbriquettes are dried and-then .coked and are charged, preferably hot as they leave the .cokingifurnace, into the upper portion ofavertical heating .chamber wherein they are heated :to complete the .reductionqof .the .zinc. The metal and gasesproduced during the reaction pass upwardly to a condenser and the Spent briquettes pass downwardly .to a .point of idischarge. The process requires elaborate equipment and -special precautions are required to :prevent ithe freshly reduced zinc-:from condensing within'the furnace zorxre- .oxidizingtto form blue powder.

' (.c) rFluiaz'zed continuous p-rocess.-As previously noted a 'more -.recently developed continuous :process involves the fluo-solidstechnique. Thus,-in Patent,-No. 2,478,912 .a process is described in which comminuted reducible =zinc compounds may be reduced by either a solid .or :a gaseous reducing agent by introducing the zinc compound into a reducing zone consisting predominantly of .a suspension of particles of asolidzdiluent in a gas. The-zinc formed by reduction passes continuously rout of the reaction vessel andis condensed. Initheaforesaid patented .process the comminuted *ZlIlCCOIIlPOUHdlS supplied'in finelytdivided form to a reducing-zone, along with:the solid diluent. A fiuidizing gaszis admitted to the lower ,.port-iontofthe reducing zone to maintain thesolidrdiluent -and zinc-containing -material in a fluidized condition.

.dense'd by suitable means.

The entire fluidized bed a is heated by suitable :means to temperatures between 1600" and "2300 F., at :which .temperatures the zinc compound is readily reduced by .carbon or carbon monoxide to form 'zinc vapor which .passes 01f along vwith carbon monoxide.

(d) Th present invention..In accordance with my invention-a .comrninuted-zinc compound is reduced by carbon monoxide in a fused bath which may:.advantageously contain carbon in finely divided form. The re sulting zinc vapor is continuously withdrawn and con- -By' continuously "feeding the ;several; reactants into thefused ,bath and by continuously withdrawing the ;products :from the system, the .entire processcan be carriedzout ina manner which isj'free from the :obvious disadvantages of r the batch type processes described-above.

Another advantage possessed "by my process, particularly when compared with either. of'thecontinuous processes .describedxabove lies in the-simplicity offthe apparat'us required as compared with the highly specialized apparatusemployed in'the prior artprocesses. Other advantages will become apparent 'from the following description.

:The mostsignificant departure from theprior art resides in the use of a fused bath ascthe environmentfor carrying out the reductionof areducible=zinc compound. The.maten'als chosen for the fused bath inust havea meltingspoint below the temperature at.which the' reduction takes .place' and at the same time must;=possess a vaporwpressure which is very low at the reaction,temperaturesl .lnaddition, in many instances, it may be found. desirable to choose as one or more. of the components :of the fused:bath material :whichxfluxes the anticipated impurities in the zinciferous rawmaterialsto'be reduced. :1 havefound that the alkali metal chlorides (are particularly suited to carrying out my process; Sodium chloride or mixtures of sodium chloride and .potassium-. chloride have been found to; possess the. desirableucombintltion of properties -.and to be readily adapted to the execution of my process. By..ernploying a fused bath as the reaction environment, previous disadvantages of the prior art resulting from the tendency of the charges to fuse or agglomerate are completely avoided. 1

The comminuted zinc compound fed into the fused salt bath may comprise either a raw zinc ore or a beneficiated zinc ore. In the event that the latter is available, for instance, in the form of a roasted concentrate, it is reduced to a finely divided powder by any suitable means in order to expedite the desired reduction reaction.

The reduction reaction is effected in the fused bath by means of a reducing gas which is sparged into the bath in very finely divided form. Any suitable reducing gas may beemployed and carbon monoxide containing mixtures have been found to be particularly effective. The reducing gas tends ,todissolve in the fused salt bath and accordingly there is obtained a reaction between gas dissolved and the solid to be reduced in addition to a reaction between the gas itself and the solid to be reduced.

In order that reducing conditions may be insured in the system, it has been found expedient to include additional carbon in the bath in finely divided form. The carbon particles are continuously agitated by the gas introduced into the melt and thus are continuously brought into contact with fresh material such as carbon dioxide formed by reduction of the zinc oxide, which the particles reduce to reform carbon monoxide.

As a result of the reaction, zinc vapor and other gaseous products are continuously evolved from the bath and are withdrawn-therefrom. The temperature of the reaction is chosen so that the zinc will have an appreciable vapor pressure and hence, it is possible to operate at temperatures below the boiling point of zinc (1706 F.) and at temperatures below those conventionally employed in this art. For example, in accordance with my invention Example A mixture was prepared by thoroughly mixing 162 parts by weight of zinc oxide, 30 parts by weight of carbon and 850 parts by weight of sodium chloride. The mixture was charged into a reaction furnace provided with heating means and heated to a temperature of approximately 850 C. (1562 F.). After the salt had melted, carbon monoxide was introduced through a porous tube, so that the gas was distributed throughout the melt. The furnace was provided with a cover having an offtake to permit withdrawal of gaseous products. The gases evolved were passed through a condenser constructed of graphite, from which a bright metallic product of elemental zinc was recovered. While the above process was run as a batch process, it could be readily converted to a continuous process.

From the above it-will be seen that my process is characterized by a number of advantages. Firstly it will be noted that the apparatus required is simple in nature. Essentially the only major units of equipment necessary comprise: a means to produce a suitable reducing gas such as water gas, producer gas, or pure carbon monoxide; a reducing furnace and a condenser. If a reducible zinc compound is not available in comminuted form obviously means must be furnished for obtaining this material. Such means could include a furnace in which zinc sulfides or other zinc compounds are converted to zinc oxide and crushing means for pulverizing the oxide product. Optionally, in the event that the zinc is collected in molten form a means for casting the zinc may be provided.

I claim:

1. A process for the reduction of a reducible zinc compound which comprises establishing a fused bath of at least one alkali metal chloride salt, introducing a zinc compound and a reducing agent into the fused bath, effecting reduction of the zinc compound in said fused bath at a temperature below the boiling point of zinc metal, recovering zinc from the gaseous effiuent from fused salt bath.

2. A process for producing metallic zinc which includes forming a fused bath consisting essentially of at least one alkali metal chloride, introducing a reducible zinc compound and a gaseous reducing agent into the fused alkali metal chloride bath, maintaining the bath at a temperature at which zinc metal has an appreciable vapor pressure and thereby effecting the reduction of the zinc compound and recovering the zinc so produced from the gaseous effluent from said fused bath.

3. A process for producing metallic zinc including forming a fused bath consisting essentially of at least one alkali metal chloride, introducing a reducible zinc compound and a carbon monoxide containing reducing gas into the fused bath, maintaining the fused bath at a temperature of at least about 1400 F., and recovering the zinc so-produced from the gaseous effiuent from said fused bath.

4. A process for producing metallic zinc including forming a fused bath consisting essentially of at least one alkali metal chloride, a reducible zinc compound and finely divided carbon, and introducing a carbon monoxide containing reducing gas into the fused bath,

maintaining the fused bath at a temperature of between about 1400 F. and 1550 F., and recovering the zinc so-produced from the gaseous effiuent from said fused bath.

5. A process for producing metallic zinc including forming a fused bath comprising sodium chloride, introducing a reducible zinc compound and a carbon monoxide containing reducing gas into the fused bath, maintaining the fused bath at a temperature of at least about 1400 F., and recovering the zinc so-produced from the gaseousefiluent from said fused bath.

6. A process for producing metallic zinc including forming a fused bath consisting essentially of at least one alkali metal chloride and solid finely divided carbon, introducing zinc oxide and a carbon monoxide containing reducing gas into the fused bath, maintaining the fused bath at a temperature of between about 1400 F. and 1550 F., and recovering the zinc so-produced from the gaseous eflluent from said fused bath.

7. A process for producing metallic zinc including forming a fused bath essentially comprising sodium chloride, introducing zinc oxide and a reducing gas into the fused bath, maintaining the fused bath at a temperature of at least about 1400 F. but not exceeding about 1706 F., and recovering the zinc so-produced from the gaseous effluent from said fused bath.

8. A process for producing metallic zinc including forming a fused bath comprising sodium chloride, introducing zinc oxide and carbon monoxide gas into the fused bath, maintaining the fused bath at a temperature of between 1400 F. and 1550 F., and recovering the zinc so-produced from the gaseous effluent from said fused bath.

References Cited in the file of this patent UNITED STATES PATENTS 37,803 Bennett Mar. 3, 1863 681,609 De Bechi Aug. 27, 1901 1,431,877 Diehl Oct. 10, 1922 1,913,929 Kerschbaum June 13, 1933 2,382,565 Hedberg Aug. 14, 1945 2,685,506 Schereschewsky Aug. 3, 1954 2,701,194 Deterding Feb. 1, 1955 2,745,736 Loevenstein May15, 1956 

1. A PROCESS FOR THE REDUCTION OF A REDUCIBLE ZINC ECOMPOUND WHICH COMPRISES ESTABLISHING A FUSED BATH OF AT LEAST ONE ALKALI METAL CHLORIDE SALT, INTRODUCING A ZINC COMPOUND AND A REDUCING AGENT INTO THE FUSED BATH, EFFECTING REDUCTION OF THE ZINC COMPOUND IN SAID FUSED BATH AT A TEMPERATURE BELOW THE BOILING POING OF ZINC METAL, RECOVERING ZINC FROM THE GASEOUS EFFLUENT FROM FUSED SALT BATH. 